Controlling drainage by addition of longs and fines to stabilize stock system

ABSTRACT

IN A FOURDRINIER TYPE PAPERMAKING MACHINE HAVING A PLURALITY OF INTERRELATED MATERIAL FLOWS INDICATIVE OF A STATE OF EQUIBRIUM, THAT EQUILIBRIUM CAN BE CONTROLLED BY CONTROLLING ONE OF THE FLOWS, NAMELY THE DRAINAGE FLOW. AN ACTUAL DRAINAGE FLOW IS METERED AND COMPARED TO A DESIRED DRAINAGE FLOW AND LONG OR FINE FIBERS ARE INTRODUCED INTO THE MIXED STOCK IN A RATIO DETERMINED BY THE COMPARISION STEP TO MAKE THE TWO DRAINAGE FLOWS EQUAL.

3,813,283 CONTROLLING DRAINAGE BY ADDITION OF LUNGS AND I y 28, 1974 J.c. URBAS FINES To STABILIZE STOCK"SYSTEM Filed March 10 1972 3Sheets-Sheet l zozE FLo w PRIOR ART i0 GrzouHDwoob b ocK J. c. URBAS3,813,283 CONTROLLlHG DRALNAGE BY ADDITION OI LUNGS AND May 28, 1974FINES TO STABIIJIZE STOCK SYSTEM 7 Filed March 10 3 Sheets-Sheet 216rzouNDwooD STOCK J. c. URBAS 3,813,283 CONTROLLING DRAINAGE BY ADDITIONOF LUNGS AND May 2s, 1974 FINES TO STABILIZE STOCK SYSTEM 3 Sheets-Sheet3 Filed March 10 1972 Ill llll l|| United States Patent 3,813,283CONTROLLING DRAINAGE BY ADDITION OF LONGS AND FINES TO STABILIZE STOCKSYSTEM John Christopher Urbas, 200 Comber Ave., Dorval, Quebec, CanadaFiled Mar. 10, 1972, Ser. No. 233,529

Int. Cl. D21f 1/60 US. Cl. 162-190 6 Claims ABSTRACT OF THE DISCLOSUREThis invention relates in general to the manufacture of paper and moreparticularly to a method for stabilizing stock induced drainagevariations at the fourdrinier.

The primary objectives of the fourdrinier process are to consistentlyfulfill certain quality requirements in the finished product and toachieve sufficient dewatering and consolidation of the web to effectready transfer to subsequent and more efficient dewatering stations.These objectives appear to be very straightforward and perhaps evenobvious. However, achievement of these objectives, even in modern mills,is far from straightforward and the techniques used are anything butobvious.

When analysing the fourdrinier portion only of the paper making process,it becomes apparent that a great number of features affect the qualityof the web as it is passed to the next section in the process. Some ofthese influencing features include: changes in fiber or stockcharacteristics such as structure, dimensions and proportions; changesin chemical and thermal characteristics; changes in the nature ofdiluent in both quantity and quality; changes in the drainageperformance of the fourdrinier due to wear and tear on equipment,plug-ups, readjustments or seasonal capacity losses; lack of reliableand accurate indicators to describe the origin, nature and severity ofchanges; heavy dependence on subjective analysis (inconsistent due torotating calibre and attitude of personnel); the fact that thefourdrinier is a composite of several highly interrelated hydrauliccircuits which are on manual control and in their ensemble areconsidered highly complex even to the devout student; and the fact thatthe fourdrinier is the most accessible area where compensations fordeficiencies in other segments of the process can be made, thesecompensations tending to reduce or hinder the tolerance of the processto other kinds of change.

In an attempt to overcome the above-mentioned problem features,palliative and/or trial and error practices are often relied upon. Thesepractices ultimately prove costly due to losses in output, quality andunnecessary furnish costs. It becomes evident that overcoming theproblem features becomes, in itself, a problem in advanced processcontrol, focused on sustaining an optimized equilibrium. The degree ofsuccess relates directly to two basic requisites of good processcontrol: (1) the timely availability of information regarding thevariables of concern, and (2) the control capability to accommodatethem. Paper making, unfortunately, continuously violates in varyingdegrees these two basic requisites.

The variations which accumulate in the finished product at the reel arecommonly referred to as being in machine direction (MD) or in crossdirection (CD). It is often 3,813,283 Patented May 28, 1974 difficult toidentify the source of the variations and even with correct diagnosis,limited correction facilities at the needed location may frequentlyimpose further restrictions since palliative action must be taken.

Overall process equilibrium might be described as that period when reelcaliper is sufliciently uniform and stable that process adjustments areunnecessary. A number of sub-equilibria influence the duration of theoverall equilibrium explaining why this duration can range from fifteenminutes to something that lasts for days. The duration and size ofchange describe the degree of process stability which is a good index ofmachine performance. Keeping changes to a minimum is papermakings majorobjective. A change, unattended, can start with quality rejects,multiply into breaks, loss due to torn-off and other rejects as thetrouble compounds itself while running its transient and elusive course.In particular, transient MD changes which are of stock origin do notlend themselves to easy solutions, at least not with existing equipment.

Attempts in the past to control the stock have been highly complex,expensive and/ or ineffective. For example in one system for controllingstock, the surface of the paper issuing from the dryers is opticallyexamined for fiber density. The obtained fiber count is compared to adesired fiber count and an error signal proportional to the differencebetween counts is generated to direct a control device which adjusts themanufacturing process of the fibrous material to provide the desiredfiber count per unit length in the manufactured material. This system isespecially disadvantageous since it must obtain its count from theessentially finished product and hence the time between detection andcorrection, when measured in terms of feet of paper manufactured,becomes economically unacceptable. The system is complex, expensive andat the high speeds employed in making paper would not be instantaneousas required.

In another example of a control system a sample of the stock is drawnoifand a measurement of the fiber length, cross-sectional area and volumeis made. The sample is diluted, an electrolyte solution is added andsignals are produced in the sensing head indicative of particle size.The signal information from the sensing head is then delivered tosuitable amplifier and control means for control of the stock input.This system also involves highly complex electronic circuitry and, likethe previous example, would not be easily adaptable toexisting'equipment. In addition the time lag between detection andcorrection would not be acceptable. Neither of these systems willreadily accommodate the usual condition where the stock includes fibersof highly variable lengths.

Yet another attempt approaches a solution for the problems encounteredwith stock having coarse (long) and fine (short) constituents. With thisprocess the mixed stock is first sifted to obtain the fine constituents,then to obtain the coarse constituents below a specific size, any leftover being ground up and resifted. Then the constituents are mixed in apredetermined and reasonably constant ratio. This should then ensure apaper of a specific desired wet strength. However this system is not afeedback system and it is concerned with the initial preparation of thestock.

There is no provision for continuously determining whether the stock isof the correct proportions and no provision for altering the stockproportions at or near the headbox in response to such a control device.

In order to achieve effective control of stock variations, one musttherefore investigate their origin, behaviour and influence.

At equilibrium at the wet end incoming stock is combined in specificproportions with recirculating fibers in the wire pit. Furnish or stockis again a difficult item to characterize but a method called FinesRatio has proven to be a satisfactory tool for this application. If thefourdrinier wire is considered as a go, no-go gauge, the fibers may bedivided into two segments; fines if they can pass through the wire andlongs if they cannot. The ratio of fines to longs is called F (FinesRatio) and is essentially an index of fiber quality. Varying theseproportions changes the properties of the paper not only at the dry endbut also the behaviour at the wet end, namely drainage rates, flowdistribution, fiber fractionation and ultimately fiber consolidation andwet sheet strength.

The mass balance (water and solids) must be maintained at all times andmay be expressed as A+B+C=W+X+Y+Z,

wherein A is mixed stock flow, B is dilution water flow.

C is shower water flow, W is the flow to the presses, X is the fiatboxflow, Y is the wirepit flow and Z is the reject flow. In setting upequilibrium, the objective is to have the dryest sheet going to thepresses with the best formation. This is achieved by the adjustment ofthe recirculation (R) and the equilibrium (E). Equilibrium asestablished may be described by the proportions of W:X:Y:Z. Asequilibrium is displaced in either direction, this results in anincreasing or decreasing W and produces a new distribution of WzX: YzZ.

vIt is apparent that there is an allowable range of equilibriumpositions, each set for a purpose and capable of a numericaldescription. All ramifications will not be explored here although thethree principal methods of displacing equilibrium should be remembered,namely 1. intentional change by flow adjustments of R, A, B

or C

2. gradual deterioration of the drainage capacity of the table 3.uncontrolled changes in stock which alter the mass balancerelationships.

Recognizing the importance of sustaining a given equilibrium it isobvious that displacements by the last method, the uncontrolled stockchange, can be a major factor in a machine's output, both in quality andrunnability.

It can be said that each machine at a given equilibrium can tolerate afixed variation in stock without atfecting runnability. This variation,termed Tolerance Quotient (TQ), may be either positive or negative andnot necessarily by the same amount. It is expressed in appropriate unitsof stock quality and is plotted vertically against time. The TQ shouldbe expected to diminish with time due to normal wear and tear, but therate of decay will vary with the service attention given the machine.This varies with the operation and deserves only passing mention sincegreater importance must be assigned to the specific TQ value at alltimes.

Peak TQ, at time zero, achieved after a thorough machine clean-up,alignment and adjustment to optimized setting is not necessarilyconsistent with every start-up. Maximum TQ settings can only be expectedoccasionally if trial and error techniques are used. This partiallyexplains why papermakers shun on-the-run adjustments and even why twosupposedly identical machines perform differently.

Occasionally adjustments are mandatory. Due to lack of controls thestock change may be large enough to exceed-the existing TQ and the sheetwill break. An intentional repositioning of the equilibrium is thenrequired to accommodate the new conditions.

Interference with equilibrium is reviewed in the preceding examples withparticular emphasis on stock originated MD variations. The followingsummary merely serves as additional emphasis on the potential whichexists in a. truly stable equilibrium.

More paper fewer machine upsets fewer breaks fewer quality rejects lesstorn-off less loss due to fewer recovery cycles higher machineeflicie'ncy fewer maladjustments like draws, steam pressure,

calendar stack cooling and heating reduced operator workload permitshigher attention to otherwise neglected areas Less cost constantconditions identify true CD profile and permit correction and raise tonew level.

stability permits use of less chemical furnish because needed margin ofsafety in'sheet strength is not needed.

Stock variations therefore trigger the majority of all production lossesand any method of subduing or eliminating them is equatable to profitgain. This incentive has fostered various developments such ascontrolled refining, selective screening, special blending, etc.

The present invention provides an automatic stock stabilizing systemwhich reduces the variables to only two, the sum of which is a constant.Thus, a variation in one results in a corresponding variation in theother, specifically in W. The system provides means for making each ofthe flows constant with two exceptions and provides a means fordetermining the proper correction required and applying that correction.The measured quantity is the drainage which is sometimes proportional tothe tages. The stock stabilizing system can be considered as r thenucleus of a sophisticated fourdrinier controller.

The stock stabilizing system of the present invention will proveeminently useful in automatically controlling a more constant productdelivery to the couch, by the reduction of slurry dewatering variationon the fourdrinier. The

Fourdrinier process will be simplified as'constant surveillance at thewet end will not be required and the machine will have greater toleranceto change. In the future, the

paper-maker will be able to identify and describe stock changes indefinitive terms and most important, the system will permit optimizingof all machine adjustments and even, in turn, to fiber cost reduction onnewsprint machines.

The stock stabilizing system of the present invention will now bedescribed in more detail and with reference to the accompanying drawingswherein:

FIG. 1 illustrates in schematic form the basic Fourdrinier process formaking paper.

'FIG. 2 illustrates in schematic form the equipment added to the basicprocess to achieve constant flows.

FIG. 3 illustrates in schematic form the stock stabilizing system of thepresent invention.

FIG. 4 illustrates in plan the control device of the present inventionand as viewed along the line 4-4 of FIG. 5.

FIG. 5 is a section in elevation looking in the direction of the sectionline 5-5 of FIG. 4.

FIG. 6, on the same sheet as FIG. 3, is a section in elevation lookingin the direction of the section line 6-6' of FIG. 4.

A preferred embodiment of the stock stabilizing system is illustrated inthe accompanying drawings. In order to better understand the invention,the basic fourdrinier process with which the present invention isconcerned is shown diagrammatically in FIG. 1.

As illustrated in FIG. 1, the stock S flows through a magmeter'20 intothe mixed stock chest 22 where it-is combined with the broke flow Br andthe groundwood G, the flow of each being controlled by a magmeter 20.The mixed stock is then pumped through pump 24, magmeter 26 and controlvalve 28 until it reaches fan pump 30. It is then pumped to the cleaners32 where it is thoroughly cleaned, any rejects exiting as Z. The cleanedmixed stock is pumped to headbox 34 from which it flows as a slice ontothe fourdrinier machine 36. This machine consists at the wet and of afine mesh wire 38 usually known as a fourdrinierwire which rolls about aseries of rolls, namely the breast roll 40, the couch roll 42 and anumber of a support and tensioning rolls or foils 44L As the web of wetpaper proceeds along the wire 38 most of the moisture originally thereinis removed through the Wire either through gravity, suction pluses, ornatural evaporation. Since the mixed stock is made up primarily offibers and water, it is useful to categorize the fibers into two groups,the fines and the longs. By utilizing the fourdrinier wire as a go/no-gogauge, fines are those fibers which will pass through the interstices ofthe wire -mesh. Inasmuch os fibers are not oriented until the web isconsiderably along the wire, the vast majority of the fines which are topass through the wire will have done so in the vicinity of the formingboards 46 thereby creating a rich white water. White water is thedrainage water containing fibers which have filtered through the wireand is richest near the breast roll, leanest near thecouch roll. Themoisture continues to leave the web all along its length, anothercollection point being the flatboxes 48 situated in front of couch roll42.

Most of the white water from the web falls into the wirepit 50 fromwhich it can be recirculated as R through to the headbox. The wirepit isformed as a constant headtank such that excess water will flow over wall52 as overflow Y into overflow tank 54. Overflow from that tank goesinto the saveall 56 which is used to reclaim fibers and fillers from thewhite water. 1

In order to prevent the wire from clogging with fibers it iscontinuously cleaned with water C flowing through shower 58. Thebombardment of the wire by water C dislodges most fibers and hence keepsthe wire clean. Make-up water is also fed into the wirepit as dilutionwater B through nozzles 60. t t 1 As previously mentioned, the desirablestate with paper machine is a constant equilibrium. The equilibrium canbe observed as a point (B) whereat a specific drainage or dewatering hasbeen achieved, say as a percent dewatering Shifting of this point duringa run is indicative of variable dewatering, due in part to a varyingfines ratio. Thus, if the drainage can be made constant, the' point ofequilibrium, will be constant.

It has already been established that the papermaking machine must obey aconservation law as expressed by the equationi p +C= +Z -(1) e i A ismixed stock flow B is dilution water flow C is shower water flow W isflow to the presses X is flatbox flow Y is wirepit overflow, and Z isreject flow Since equilibrium maybe described by the proportions ofW:X:Y:Z, it becomes desirable tomake as many of the flow variables aspossible constanLIn fact equation (1) may be reduced to the form; I

To begin with, the flow A can be rendered constant through magmeter .26.This immediately reduces the equation to where K is constant. In orderto make X constant, the

water from imput means including flatboxes 48 and conduit 85 is fed intoa head tank 62 which has a number of portions, namely 64, 70 and 72therein. A constant head portion 64 receives the flow X, a constantamount X being drawn off to white water tank. This water may be usedelsewhere in the papermaking process, and the tank has associatedtherewith pump 68. The overflow from portion 64 is fed into constanthead tank 70 from which a constant amount X is drawn oil. The remainderof flow X overflows into portion 72 from where it is recycled as X, intothe mixed stock. Thus, since fixed portions of X are drawn off fordesired functions and the variable remainder has been returned to thesystem, the flatbox flow X has been made constant with respect to theoverall process. In order to make B+C constant, constant flow X is fedinto head tank 74. A constant head portion 76 provides a constant flowto the showers 58 and the overflow also constant goes to the dilutionnozzles. The equation where K =K +Z=constant.

A variation in the wirepit flow Y is thus an indication of the fiow Wsince K will have a specific value for each grade of paper on a specificmachine. Flow W is diflicult of itself to measure accurately, but not sowith Y, hence the simplified equation can be extremely useful to thepapermaker. He very quickly has an accurate measurement of W and is thenable to utilize many well-known techniques to keep W constant.

' A new method for keeping W constant under most circumstances is thestock stabilizing system of the present invention which has the primarytask of maintaining equilibrium through maintaining a constant drainagerate. In most situations a variation in W will be accompanied byavariation in the drainage rate and hence will be accommodated by theensuing correction therein. Only in special cases will the papermakerhave to resort to additional techniques to re-establish W.

' As mentioned above, the goal is a constant equilibrium point, measuredas a constant drainage or sometimes by a constant fines ratio. Itbecomes apparent that in order to maintain a constant drainage rate, itwill be necessary to be able to alter the actual quantity of fine orlong fibers 'in the mixed stock to thereby return a varying drainagerate to its desired value. It should be pointed out that the, drainagerate is directly related to the quantity or ratio of fibers in the mixedstock as a greater number of fines, for example, in the stock will lowerthe drainage rate and vice versa.

To that end the stock stabilizing system has been developed. It isillustrated schematically in its simplest or basic form in FIG. 3.

In order to vary the drainage rate of the mixed stock, it is firstnecessary to have a source of long and fine fibers for addition to themixed stock. Once the source has been established, means to selectivelymeter requisite fibers to the mixed stock is required. In the presentinvention such a means is control device 102 which will be described indetail later. It suflices to say that control device 102 will, when itsenses a variation in the drainage introduce the' appropriate' fibers,into the-mixed stock to -re-establish the fines ratio. Irrthis sense,the stock'stabilizing system is a feedback system with a practicallyzero "time lag. v

However, for the, control device 102 to be effective it mus ang have a'source of long and line fibers. As dis- "cftissedpreviously, finesforsthe' most part drop through the .iourdrinier wire 38 ashort distancebeyond breast mull), a forming" boards, 46. n1 seamen [t the lines,fmost jof the'lwa'tpr from the web descends h through the wire' inthisarea and hence the resulting solution is rich in fines, i.e., rich'white water? The rich white water extracted from the formin'glvboardsis} taken to head i tank 90, a'fixed amount p n-g drawn .ofi fromconstant head portion 92tor transmittal tothe control device 102.-. "Theoverflowfrom portion 92 chllects in portion9 4, from i which it isrecycled into theinixed stock as shown byfthe arrowed flow lines. Thusa'supp'ly of fines is made, availa'bleto the control device.-

I W Inorder to provide a supply-of longs, a small portion of the mixedstock is extracted therefrom. and introduced into the constant headportion 98 ofhead' tank'llti The factual amount of mixed stock drawnofiwill vary depending' on 'machine size and grade'of paper beingproduced. In some instances an amount of 2% may be" sufiicient to meetthe needs of the system. Inasmuch as this stock is rich in fines as wellas longs and is of a high fiber consistency, it is necessary to dilutethis stock to essentially the same consistency as the rich white waterin head tank 90. While any warm, clean Water would sufiice as adilutent, it is convenient to utilize the lean white water in head tank62. Thus, an additional constant head portion 88 is provided in headtank 62 to catch the overflow from portion 70 and to supply a constantHow of lean white water X,, for diluting the stock from tank 96."

As shown schematically in'FIG. 3 dilution occurs at point 112, thedilute solution being then fed into control device 102.

The control device 102 is shown schematically ascorbprising fourcompartemnts 104, 106, 108 and 110. Com partment 104 receives the longfibers, compartment 106 receives the fines and compartment 108dischargefs" the appropriate quantity of either back' into the mixedstock to adjust the fines ratio. Compartment 110 takes the rejects fromcompartments 104 and 106 and returns them to the" save Compartments 104and 106 are rotatable together or as a unit through 90 clockwiseorlcounterclockwise to present a variable quantity of fines or longsrespectively to compartment 108. When in the neutral location, the ratioof fines to longs compartment 108" is identical to thefines ratio of themixedstock,

It should bereadilyapparent that the stock, stabiliai ng system hereindescribed is an automaticlsystem, with practically instantaneousresponse, The ,inputof fi lgers to the mixed stock from the controldevice. maybeponstantly changing, but nevertheless the drainage: rateremains constant." Without the simplifiedfiow equation; this would beimpossible since the number of variables would be overwhelming and"problems would only multiplyw With the simplified" flow equation, the'I'pa' rlerrnaking 'process at the fourdrinier can be readily controlledand inmost instances screen the flow W to the couch.

The basic stock stabilizing system has ""been"'"herein described, but itis readily apparent that it can belmodified I to suit particular needs.As already mentioned, mixed stockmay be diluted with lean white waterforev fi'with fresh water. This reduces the fines content in the entralsegment. of the long fiber control component. 7

option, a filter device can be added in m gnet-Bar a ns:

.to remove and concentrate fines. These fines conld: be

.:then added to head tank 90-to increase the-concentration of the lowfreeness circuit while reducing the fines concentration in thelong-fiber component. Thus,the dimer-- l ential between fines and"greater, therebyexpanding the range 8 long concentrations would beof-the unit:

1 Additional options include:

I (l)" the installation of an adequate groundwood source ahead orMagmeter 26 to permit readjustment of the stock quality when'needed' byreduction or addition of groundwood or other furnish;

(2) the installation "of a fines recovery system to' accumulate 'thevariance in fines and to ire-introduce the stored quantity at theneeded'rate to the stock system;

""(3) {the provision of a complete wet end' control centre withcertaininstnnnents which when added to the foregoing can reasy" upgrade thevalue (of the equipment and provide a controlpackage for the completemachine; and

f (4) the" provision of means for rneasuringair flow on the last dry boxat constant vacuum to p identify changes in ft'arrnation, as well asbasis 'weight.

These modifications are illustrative of the manners in whichthesystemcan: bealtered" to suit theneeds of a ,particular mill, They areonly described herein and are .not shown in the drawings, as there areundoubtedly many other options of modifications possible.

A more detailed configuration for the control device is illustratedin-F1GS.4, 5 and 6- the main features ofa .preferred embodiment beingshown therein. Only the :basic preferred embodiment of the controldevice is shown. Ancillary features and components of the entire systemare not illustrated as they are merely matters of design expediency andwill only draw mention herein.

Control device 102 consists of three basic components, a distributor113, a collector 117 and a separator 136.

Distributor 113 is essentially a cup-shaped container havingcylindricalwall 114 and an end or bottom wall 115. At the open end of the cylnder,a downwardly and outwardly projecting flange 116 is circumferentiallyafiixed.

The entire container can be rotated about its longitudinal axis when anappropriate motive source is attached to shaft.160. An effective motivesource. might involve a i rack and pinion arrangement, with the pinion161 mounted coaxially on shaft 160. A suitable bearingmust,

.of course, be provided tor etfective rotation.

The container is divided into chambers 104 and 106 by a plate 138 andseparator 136. Plate 138 is sealed, as by welding, along its outer edgesto the inside surfaces of wall114 and bottom It has a central cutoutformedtoaccept the separator 136 to. which itis fixedly l sealed, as byvwelding, Plate, 138 may extend upwards beyond the open'end of thecontainer so as to ensure that there is no cross-spillage betweenchambers 104 and 106. 11h addition,: ..pla t'e' 138,, may be equippedwith a horizoiital extension 140"which projects outwardly over flange116. Attached to extension 140 is separator blade 142 whiohitfittedsealingly to move in compartment 110 as separator 136 rotates. Thepurpose of blade. 142 will become apparent inthe ensuing descriptionof'the operation of the control device.

always directed tothe appropriate compartment, 104 or '106.-To that end,separator 136 is of an essentially cylindrical shapeg'its diameter beinglarge enough so that downwardly directed flow pipes 152., 154 and'156discharge their flows into the separator without any flow being directedoutside its confines. The flow from pipes 150,154 and '156 is alwaysmixed in the remaining portion' of the separatonthe' resulting flow ofmixed constituents exiting from discharge hole 144 located in the bottomof separator 136 and being directed into compartment 104. Withinseparator 136 is a downpipe 146, its internal diameter being greaterthan the external diameter of pipe 150'. The entrance to downpipe 1 46is concentric with separator 13-6 and the pipe is directed verticallydownwardly towards the bottom. A short distance above the bottom thedown pipe is directed to the cylindrical surface of separator 136,exiting into compartment 106 through opening 148. Thus, as separator 136rotates, the fluid from pipe 150 always enters the separator along itsaxis, but exits laterally thereof.

The remaining component of control device 102 is collector 117. Thecollector, as its name implies, collects fluid overflowing over flange116 from distributor 113. It consists of an annular trough 118completely surrounding distributor 113 and positioned such that itsinside wall is underneath flange 116. Trough 118 is separated intocompartments 108 and 110 by diametrically opposed plates 134.Approximately mid-way between plates 134 in compartment 108 and in thebottom of trough 118 is an opening 120 which exits into funnel 122,downpipe 124 and accept pipe 126. Each plate 134 includes a steppedportion 128 lying within compartment 108 and eifectively extendingcompartment 110 thereunder. In the bottom of trough 118 and under eachstep 128 is a hole 130, one of which exits into return pipe 131, theother exiting into return pipe 132.

The operation of the control device 102 will now be described. Pipe 150carries in it a constant flow of rich white water from head tank 90.With the separator 136 and distributor 113 positioned as in FIG. 4, therich white water will flow through downpipe 14.6, hole 148 and fillcompartment 106 until it overflows, 50% going into collector compartment108 and 50% going into collector compartment 110. The mixed stock entersseparator 136 from head tank 96 via pipe 156 and is mixed in theseparator with lean white water entering from head tank 62 via pipe 152.If required extra lean white water for dilution may be introduced viapipe 154. The high freeness stock of desired dilution exits fromseparator 136 through hole 144 into compartment 104. Again with theconfiguration as in FIG. 4, 50% of the overflow from compartment 104enters collector compartment 108 and 50% enters collector compartment110. Blade 142 cffectively separates the rejected long fibers incompartment 110 from the rejected fines therein. Thus, the fines can bereturned via pipe 132 to head-tank 90 and the long fibers can bereturned via pipe 131 to head tank 96 or to wherever they may berequired.

In the FIG. 4 configuration, the control device is in its neutralcondition as the consistency of the flows in compartment 108 whichultimately is reintroduced into the mixed stock is the same as theconsistency of the mixed stock. The flow collected'in compartment 110 isreject and may be directed to saveall 56 for reclamation of the fiberstherein. If, however, meter 86 senses a change in the drainage rate offlatboxes 48, a change in the consistency of the mixed stock hasoccurred and must be overcome. By known comparison and transducer meanssuch as 87 the change in drainage rate is quantified and translated intoa rotation of distributor 113 and separator 136. If, for example, themeter indicates a deficiency of fines in the mixed stock, distributor113 and separator 136 rotate clockwise (FIG. 4) such that more overflowfrom compartment 106 than from compartment 104 into compartment 108 willoccur. Thus the flow from compartment 108 through accept pipe 126 willbe richer in fines than in the neutral state and the deficiency in themixed stock will be accommodated. Correspondingly the reject flow willbe rich in long fibers as compartment 1'10 will receive most of its flowfrom compartment 104. Thus most of the reject flowwill be exiting viareturn pipe 131.

It should be borne in mind that the control device herein described neednot be restricted to its present application. It could be effectivelyutilized in most situations where the mixing of liquids in a controlledrate is required. It need not be used solely in a stock stabilizingsystem as herein disclosed.

The embodiments of the invention in which an exclusive property orprivilege is claimed are defined as follows:

1. In a fourdrinier type papermaking machine in which the papermakingprocess is defined by the equation A+B+Cl=|W+X+Y+Z where A represents aflow of mixed stock, of fine and long fibers of a predeterminedconsistency, B represents a flow of dilution water, C represents a flowof water to a set of showers, W represents a flow of paper to a couch, Xrepresents a flow of drainage water, Y represents an overflow from saidwirepit and Z represents a flow of rejects, said flows being indicativeof a state of equilibrium in said machine, a method for controlling saidequilibrium comprising the steps of (a) rendering flow A constant;

(b) dividing flows X, Z into constant portions X 2;;

and variable portions X,, Z, respectively and reintroducing saidvariable portions into said mixed stock;

' (c) dividing said constant portion X into at least two constantportions, one of which is a sole source of water for said flows B+C,thereby rendering said flows B+C constant;

(d) metering said flow X;

(e) comparing said flow X to a desired drainage flow;

and

(f) introducing additional fine and long fibers into said mixed stock ina ratio determined by said comparing step to make said flow X equal tosaid desired drainage flow.

2. A method according to claim 1 wherein said step of dividing flow Xcomprises the step of directing said flow X to a first head tank fromwhich said constant portion X is drawn and said variable portion X, isreturned to said mixed stock.

3. A method according to claim 2 wherein said additional long fibers areobtained by diverting a portion of said flow A to a second head tank anddiluting said portion of flow A with clean water and wherein saidadditional fine fibers are obtained by diverting drainage water rich infine fibers from said machine to a third head tank.

4. A method according to claim 3 wherein said clean water is a constantportion X of said constant por- I101! xx- 5. In a fourdrinier typepapermaking machine having a plurality of interrelated material flowsindicative of a state of equilibrium and wherein said flows include aflow of mixed stock of fine and long fibers of a predetermined desiredconsistency, a desired drainage flow and an actual drainage flow,apparatus for controlling said equilibrium comprising metering meansconnected to said machine for metering said actual drainage flow, inputmeans connected between said machine and said metering means to conductsaid drainage flow to said metering means, comparison means operativelyconnected to said metering means for comprising said actual drainageflow to said desired drainage flow, extraction means connected to saidmachine to remove a small amount of said fine and long fibers therefrom,separate source means each having at least two compartments andconnected to said extraction means to store said small amounts of fineand short fibers separate from each other and control means responsiveto a signal generated by said comparison means, said control meanshaving mixing means connected to said source means to mix said fine andlong fibers in a ratio determined by said comparison means andintroduction means connected between said mixing means and 1 saidmachine to introduce the mixed fine and long fibers into'said'rnachinetomake said actual drainage fiow equal to said desired drainage flow.

6. In a fourdrinier type papermaking machine having a plurality ofinterrelated material flows indicative of a state of equilibrium andwherein said flows includea flow of mixed stock of fine and long fibersof a predetermined desired consistency, a desired drainage flow and anactual drainage flow, apparatus for controlling said equilibriumcomprising metering means connected to said machine for metering saidactual drainage flow, input means connected between said machine andsaid metering means to conduct said drainage flow to said metering meanscomparison means operatively connected to said metering means-forcomparing said actual drainage flow to said desired drainage flow,extraction means connected to said machine to remove a small amount ofsaid fine and long fibers therefrom, separate source means each havingat least two compartments and connected to said extraction means tostore said small amount of fine and short fibers separate from eachother and control means responsive to asignal generated by saidcomparison means, said control means including a first receptacle havingtwo first compartments, each receiving a dilute flow of said fine orlong fibers, a second receptacle adjacent said first receptacle andhaving at least two second compartments therein, overflow directingmeans connected to said first compartments for directing an overflow ofsaid dilute flows from said first to said second compartments, saidfirst receptacle being movable with respect to said second receptacle tovary the ratio of mixing said dilute flows 2 in said secondcompartments, means tor'movi'ng said first receptacle with respect tosaid secondrece'ptacle and introduction means connected between one ofsaidsecond compartments and said machine to introduce the mixed fine andlong fibers into said machine to 'malte said actual drainage flow equalto said desired drainage flow.

References Cited 7 UNITED STATES PATENTs v01. 47, No. 4 (April 1964),pp. 181Al88A-;"Dig. #6.

J. P, Casey, Pulp and Paper, 2nd edition, vol. 'II'; IntersciencePublishers, Inc New York, 1960, p'. 769. i I

s. LEoN BASHORE, Primary Examiner" M. s. ALVO, Assistant Examiner us.01. x.R.

